The present invention relates to steering. More particularly, the invention relates to steering towed mobile vehicles by remote control.
As used herein, the term "axle" is defined as a shaft which connects wheels located on opposite sides of a frame which is supported by the shaft and by sorings connected thereto. The term "short axle" is defined as a shaft which connects a pair of wheels located on the same side of the frame. The term "spindle" is defined as a short conical shaft on which a wheel is mounted.
The term "fixed axle" is defined as an axle the orientation of which remains unchanged with respect to a frame which the axle supports. The term "steerable axle" is defined as an axle which is capable of changing direction with respect to and independently of a frame which the axle supports. The term "fixed wheel" is defined as a wheel the orientation of which remains unchanged with respect to an axle on which the wheel is mounted. The term "steerable wheel" is defined as a wheel which is capable of changing direction with respect to and independently of a fixed axle to which the wheel is connected by a spindle.
Trucks, tractors, and trailers are well described in the Encyclopaedia Britannica, volume 18, pages 721-723, hereby incorporated by reference.
Tractor-trailer combinations known as "eighteen-wheelers" present special problems. FIG. 1 shows a top plan view of an eighteen-wheeler generally denoted by the numeral 9. The frame 10 of a trailer 2 is supported near the front by the frame 7 of a tractor 1. The frame 7 is supported by a fixed front axle 4 provided with a pair of steerable wheels 3 mounted on a pair of spindles 6, and by two fixed rear axles 4, each of which is provided with two pairs of fixed wheels 3a. The trailer frame 10 is further supported by two fixed axles 4 near the rear of the trailer 2. Each of these rear axles 4 is likewise provided with two pairs of fixed wheels 3a. A "fifth wheel" 8 is fastened to the frame 7 of the tractor 1.
There are serious disadvantages inherent in the present design of eighteen-wheelers:
(1) Because the only axles supporting the frame 10 of the trailer 2 are the two rear axles 4, approximately half the weight of the trailer 2 is borne by the frame 7 of the tractor 1. An immediate consequence of this burden on the tractor 1 is that tractors pulling eighteen-wheelers must be large, heavy, and rugged enough to bear about half the weight of the trailer and of the payload, as well as the weight of the tractor itself. Clearly, if part of this extra weight could be borne by the trailer, it would be possible to utilize lighter and less expensive tractors. Furthermore, the portion of the fuel utilized to move the tractor could be considerably reduced, leading to even greater savings and to a significant advantage in fuel economy and energy conservation.
(2) Because there are only fixed wheels 3a supporting the trailer 2, it is impossible for the trailer 2 to turn without some of the wheels 3a skidding or dragging to some extent. The farther apart the rear axles 4, the more serious is the problem of wheel drag. This problem causes loss of control, wasteful loss of rubber from the tires mounted on the wheels 3a, and wasteful loss of the extra energy required to overcome sliding friction as opposed to rolling friction. The trailer 2 is unstable in a turn. The faster and sharper the turn, the greater the instability.
(3) The fifth wheel 8 of the tractor 1 furnishes a leg to support the front end of the trailer 2. However, it does not furnish full support for the full width of the front end of the trailer 2. This deficiency causes the bed (not shown) of the trailer 2 to rock down on one side and up on the other side. The extent to which such rocking occurs depends on the turns that the trailer 2 makes, the imbalance of the load (which can be caused by shifting of the cargo in transit), road conditions, and other variables. This particular type of instability is almost continuous while the eighteen-wheeler 9 is in motion.
(4) Often the longitudinal center of the trailer, when loaded, is in continual up-and-down motion. This motion contributes to the instability of the trailer 2, and may in extreme cases cause the trailer 2 to collapse at the longitudional center.
(5) The looseness of the trailer king pin (not shown) in the fifth wheel 8 of the tractor 1 causes some shock, which contributes to a deficiency in traction and to a rough ride for both cargo and driver.
(6) Tandem axles are not equivalent to two single axles. Transportation authorities do not allow as much weight to be carried by a pair of tandem axles as by a pair of single axles.
(7) Tandem axles on either the tractor 1 or the trailer 2, because they drag in a turn, can individually or in combination initiate a slide of the eighteen-wheeler 9 into a "jack-knife."
(8) The trailer 2 cannot independently furnish braking for the trailer 2 and its payload (not shown). The push of the trailer 2 against the tractor 1 when brakes are applied to the tractor 1 causes the tractor 1 to yaw.
(9) There is nothing between the trailer 2 king pin (not shown) and the rear axles 4 of the eighteen-wheeler 9 to function as a load-bearing stabilizer for the trailer 2. It is part of the function of the massive tractor 1 to counteract the sideward pull of the trailer 2 upon the tractor 1 when the tractor 1 changes direction at highway speeds. The sharper the turn, the greater is the pull.
(10) The existance of the problems just enumerated has caused the gradual emergence of heavier and massive tractors 1. These massive tractors 1 have larger engines. The role of the tractor 1 is to pull, to steer, and to give stable traction to the eighteen-wheeler 9 while carrying its cargo at highway speeds. The heavier tractors 1, along with Transporation Department load limits on tandem axles 4, cause the eighteen-wheeler 9 to carry less of a payload. The increased horsepower of the tractor 1 engines (not shown) causes less fuel efficiency. These factors, in combination, raise the cost per ton-mile of freight substantially.
In an attempt to alleviate these problems, prior-art devices have utilized steerable axles with fixed wheels for eighteen-wheelers; see, for example, U.S. Pat. Nos. 3,149,858, 3,533,644, 3,712,641, 3,734,538, 4,120,509, 4,244,596, and 4,463,966. Special devices have also been devised for steering goose-neck trailers, the devices including steerable short axles, wheels steered by friction against the road, and rear wheels forcibly steered from the fifth wheel of the tractor.
These prior-art devices are expensive to manufacture and maintain; and, because of their specialized design, of limited utility. Additionally, the devices and methods described in these patents are not effective for negotiating high-speed turns on highways and public streets. They are, moreover, difficult to connect and disconnect. More specifically, when steerable axles are used to make a turn, the base of support provided by the axle is diminished proportionately to the degree of the turn.